Coaxial line attenuator



June 16, 1959. M. DOLlN EIAL 2,891,223

' COAXIAL LINE IATTENUATOR Filed Nov. 15, 1954 2 Sheets-Sheet 1 IINVENTORS 'MflPT/N Dal. IN

llnited States Patent to Applied Research Inc., Flushing, N.Y., acorporation of New York Application November 15, 1954, Serial No.468,818 9 Claims. Cl. 333-81) This invention relates to attenuators forelectric circuits and more specifically concerns a fixed pad attenuatorfor insertion in high frequency circuits to attain a predeterminedreduction in signal level.

High frequency attenuators heretofore have posed a serious problem tothe electronic industry because elec trical or mechanical disturbancesof a transmission line may produce substantial power losses through theproduction of standing waves therein. Attenuators are generallyconnected in series with a transmission line and include variouscombinations of resistive and reactive components. In order to obtainsatisfactory results and a reasonably low standing wave ratio,considerable effort has been made to attain a high degree of impedancestabilization and symmetry with the result that present knownattenuators are relatively large, cumbersome and expensive. In additionincreases in frequency further aggravates the attenuator problemparticularly in coaxial transmission lines and in such cases even thesmallest deviations from true symmetry will result in substantial powerlosses.

Accordingly one object of this invention is to provide an improvedattenuator particularly useful in connection with coaxial transmissionlines that will provide an exceedingly good standing wave ratio atfrequencies of the order of 3,000 megacycles and even higher.

.Another object of the invention is a new and improved'high frequencyattenuator having an improved voltage standing wave ratio and that ischaracterized by its simplicity, ruggedness and stability.

.Still another object of the invention is to provide an' attenuator thatmay be readily inserted in a coaxial line, that .will maintain itsaccuracy over extended periods of time and may be arranged and designedto provide a predetermined impedance and attenuation that will besubstantially uniform for frequencies up to and even exceeding 3,000megacycles.

i The above and other objects of the invention will become more apparentfrom the following description and accompanying drawings forming part ofthis application.

In the drawings:

Fig; 1 is an enlarged perspective view of a coaxial connector embodyingan attenuator in accordance with the invention;

.;.Fig. 2 is an exploded view of the connector shown in Fig. 1;

jFig. 3 is a cross sectional view of the embodiment shown in Fig. 1;

. Figs. 4 and 5 are cross sectional views taken along the lines 44 and5-5 of Fig. 3; and

Fig. 6 is a circuit diagram of the embodiment of the inventionillustrated in Fig. 1.

While the embodiment of the invention now to be described has beenillustrated in the form of a connector for coaxial high frequencytransmission lines, it is apparent that certain features thereof areequally applicable to other types of connectors such as those usedholding the terminal 47.

C Patented dune 16, 1959 in connection with open or unshieldedtransmission lines. The attenuator in the illustrated embodiment of theinvention is contained within a housing 10 consisting of male and femaleconnector parts 12 and 14 respectively which are coupled one to theother to form a substantially unitary device for insertion in serieswith a line. The male connector portion 12 is in the form of a bayonetplug and comprises a substantially cylindrical'metal body 16 having aknurled flange 18 at one end thereof and an enlarged cylindrical section20 extending from the other side of said flanged portion 18. Within thecylindrical section 16 of the male connector is a tubular insulatingmember 21 having an enlarged section 22 which closely fits the internalcontour of the cylindrical portion 16 and is held in place therein by atleast two indents 23 which engage corresponding depressions in theenlarged section 22. Within the forward cylindrical portion 21 of theinsulating member 21 is a hollow terminal member 24 having an enlargedportion 25 which cooperates with the corresponding opening in theinsulator 21 to hold the terminal in alignment therein. The forwardtubular portion .26 of terminal 24 is slotted to form a spring clip toreceive a cooperating pin in a female connector of the type shown in theconnector part 14.

The cylindrical member or sleeve 16 of the male connector part isprovided with a pair of bosses or pins 27 adapted to engagecorresponding grooves in a cooperating female connector to Secure it inposition therein.

The female connector part 14 is adapted to receive a male connector ofthe type illustrated at 12 and has an inner cylindrical member 30 ofbrass or other suitable conductive material. A sleeve 31 integrallyformed with member 30 and extending forwardly thereof is provided with aplurality of longitudinal slots 32 and is of adiameter that will form afirm mechanical and electrical connection with the body of a cooperatingmale connector similar to the connector 12. Rearwardly of the bodymember 30 is an integrally formed tubular section 33 having a. diameteridentical to that of the tubalur section 20 of the male connector part12 as previously described.

- Surrounding the body part 30 and rotatablymounted thereon .is abayonet sleeve for cooperating with and attachment to the male connectorpart to hold it in engagement with the female connector. This sleeve 34is held in position on the body part 30 by an enlarged section 39bridging a pair of washers 35, and 35 with the washer 35 being setin agroove 36 in the'housing part 30 and the washer 35' being held against ashoulder 37 by means of an intervening spring member 38. The

forward edge 40 of the enlarged section 39 is held in spacedrelationship to the washer 34 by a spacer of insulating material 41 andthe rear edge 42 of this enlarged section 39 is rolled over the outeredge of the washer 35 to secure the entire assembly in position on thehousing 30. With this arrangement the sleeve 34 can be rotated and movedforwardly against the action of spring 38 so that a firm connection witha male connector will be secured. The cylindrical part 43 of the sleeve34 is provided with a pair of helical slots 44 to receive the pins 27 ofa male connector 12 and in order to insure rigidity of the outer endthereof a flanged dinal portion 44 of the slots 44 will not breakthrough the outer surface of the flanged portion 45 as may be observedin Figs. 1 and 2.

Within the body member 30 of the female connector 14 is a tubularinsulating member 46 for receiving and It is held in place withinthehousing 30 by two or more indents 46'. The terminal 47 has anenlarged portion 48 which is received in an opening 49 in the insulator46 and lies against the inwardly extending flange 50. The tubularsection 52 of the insulator 46 extends forwardly to a point spaced fromthe end of sleeve 34 and surrounds the elongated connector pin 51 whichhas a pointed end part to facilitate engagement with a terminal such as.terminal 24 discussed in connection with the male connector part 12.

The internal diameter of the insulator section 52 surrounding the pinportion 51 is slightly greater than the outside diameter of the section2.1 of the insulator 21 in the male connector part 12 so that when amale connector similar to connector 12 is coupled thereto a firmmechanical and electrical connection will be secured with asubstantially water tight seal therebetween.

In accordance with the invention the electrical attenuator whichcomprises three resistors 53, 54 and 55 is housed within a sleeve 56 ofmetal, plastic or the like disposed within the cylindrical. portions 20and 33 of the connectors 12 and 14 respectively. The resistors arearranged in parallel relationship one to the other and connected to forma pi network as shown in Fig. 6. The resistor 54 of this network isconnected directly between the terminal members 24 and 47 andconstitutes the series resistor of the pi network. The terminal 26 isconnected through resistor 54 to the casing or shield which in thepresent embodiment constitutes the metallic bodies of the connectors 12and 14 and the resistor 53 is: connected between the terminal 47 and.the connector bodies. The terminal leads 53' and 55' of the resistors 53and 55 respectively are brought out through slots 57 and 58 which areformed in the cylindrical sections 33 and 20 of the two connector parts,respectively. Thus in the assembly of the device as may :be observed inFig. 2 the resistors are coupled one to the other and to the terminals26 and 47 as described. The metallic sleeve 56 is then slipped over theresistor and the connector parts 12 and 14 are positioned in place overthe sleeve 56. This automatically positions the terminals 26 and 47within their respective connectors and leads 53' and 55 will extend outthrough the slots 57 and 58. If desired the connector parts may besoldered together whereupon the leads 53 and 55' are then soldered tothe bodies of the connectors to complete the wiring. It will be observedthat with the disposition of the three resistors in this way asymmetrical attenuator is provided. By properly selecting resistorshaving the desirable physical size capacitive. reactances will bemaintained at a minimum and a substantially pure resistive attenuatorwill be secured. If desired the. leads 54' and 54" extending from theresistor 54 may be provided with a suitable insulating material to avoidany possibility of short circuits.

Although any suitable type of resistor may be employed in theattenuating network, composition carbon resistorsare preferred. in orderto avoid inductive effects. Such a resistor may comprise carbon granulesmixed with a suitable phenolic compound and compressed or molded to formaunitary body with the connecting leads securely embedded therein.

Theaccuracy'of an attenuator, as is Well-known, is de pendentv upon theaccuracy of the individual elements comprising it and. since. theimpedance of an attenuator in applications of this'character isimportant in order to obtain a good standing. wave ratio, it is not onlyim portant that the resistors. maintain their proper values relative oneto. the other but should maintain a desired absolute value in order thatthe. impedance of the net. work will not vary.

It has been found that by properly treating and preparing compositioncarbon resistors, extremely high accuracies and stability can beobtained. To this end the resistorsto be embodied in a given network areselected with values somewhatbelow the desired computed values.

The resistors are then preferably baked at about degrees centigrade fortwo separate periods of about ten to fifteen minutes each thoughequivalent procedures may be employed. Baking the resistors in this wayhas been found to stabilize them and prevent them from changing valuewith age. After the stabilizing process the resistors are then adjustedto the proper value by grinding away a portion of the surface to leavean intended section therein. After the desired resistance is secured,each resistor is then preferably coated with a suitable temperature andmoisture resistant coating such a glyptal or other suitable plastic andthen baked for a period of about ten minutes at a temperature of theorder of 100 degrees centigrade. The resistors are then cooled andchecked to be sure that the proper resistance has been maintained. Whilethe resistors need not be coated with an insulating compound asdiscussed above, such a procedure is preferred as it affords bothchemical and electrical protection.

The attenuator as described above has been found to produce standingwave ratios of less than 1.07:1 at frequencies up to and exceeding athousand megacycles and comparatively good ratios as high as threethousand megacycles. At lower frequencies standing wave ratios of theorder of 1.04:1 are readily obtainable. These attenuators have also beenfound to maintain their characteristics and over long periods of timewith little change in the standing wave ratio and provide a sturdydependable device that will readily withstand severe mechanical shockand substantial changes in ambient temperature without adverse effectson its operation.

While only one embodiment of the invention has been described, it isapparent that modifications, changes and alterations may be made withoutdeparting from the true scope and spirit thereof.

What is claimed is:

1. An attenuator comprising a housing of electrically conductivematerial having an elongated opening there'- in with said opening beingsubstantially symmetrical about its axis, and an electrical attenuatornetwork within said opening and formed of at least three physicallycoextensive elements disposed symmetrically about said axis with atleast one of said elements physically connected to said housing, saidhousing including terminals on each end thereof interconnected with:said net'- work.

2. An attenuator according. to claim 1 wherein the interconnectionsbetween said terminals and said network are at least partially enclosedin dielectric sleeves.

3. An attenuator comprising a pair of coaxial connectors each having atubular metal body and a centrally disposed connector terminal insulatedfrom said body, a cylindrical member of conducting material having anopening extending therethrough which is symmetrical about its axis, saidmember joining said connectors one to the other in spaced relationshipto form a substantially unitary structure, an annular electricalattenuator network having at least three physically coextensive elementsdisposed within and symmetrically about the axis of said opening atleast one electrical: connection between said elements and saidstructure and a connection between each of said termin'alsand saidnetwork.

4. An attenuator according to claim 3 wherein said coextensive elementsare resistors, with one resistor connected between said terminals andthe other resistors each being connected between one-of said terminalsand said structure. 7

5. An attenuator comprising a male coaxial connector having a tubularbody part of conductive material extending rearwardly thereof and acentral insulated terminal, a female coaxial connector having a tubularbodypart of conductive material extending rearwardly thereof and acentral insulated terminal, said tubular body parts of said connectorseach having at least one longitudinal slot therein and positioned end toend to form a substantially unitary structure, a sleeve of conductivematerial within said joined tubular body parts, and an attenuatornetwork within said sleeve, said network having at least threephysically coextensive elements symmetrically disposed about the axis ofsaid sleeve, at least one electrical connection between said network andsaid sleeve and electrical connections between each terminal and saidnetwork, said elements and sleeve forming a mechanically symmetricalnetwork interconnecting said coaxial connectors.

6. An attenuator comprising a male coaxial connector having a tubularbody part of conductive material extending rearwardly thereof and acentral insulated terminal, a female coaxial connector having a tubularbody part of conductive material extending rearwardly thereof and acentral insulated terminal, said tubular body parts of said connectorseach having at least one longitudinal slot therein and positioned end toend to form a substantially unitary structure, a sleeve of conductivematerial within said joined tubular body parts, and a resistiveattenuator within said sleeve, said attenuator having three elongatedresistors disposed in parallel physically coextensive relationship oneto the other and having leads extend from the ends thereof with oneresistor being connected between said terminals, the second resistorhaving one lead connected to the male terminal and the other leadextending through the slot in said female connector and secured to theouter surface thereof and the third resistor having one lead connectedto the female terminal and the other lead extending through the slot inthe male connector and secured to the outer surface thereof, saidresistors and sleeve forming a mechanically symmetrical network couplingsaid coaxial connectors.

7. An attenuator according to claim 6 wherein said sleeve is of metaland said connectors are provided with means for removably attaching themto cooperating connector elements.

8. An attenuator according to claim 6 wherein said resistors aretemperature stabilized non-inductive elements.

9. An attenuator according to claim 6 wherein said resistors are moldedcarbon, temperature stabilized elements.

References Cited in the file of this patent UNITED STATES PATENTS2,405,449 Robinson et al. Aug. 6, 1946 2,416,599 Victoreen Feb. 25, 19472,423,461 Meahl July 8, 1947 2,429,401 Davis Oct. 21, 1947 2,451,201Clark Oct. 12, 1948 2,579,090 Freeman May 20, 1952 2,760,170 May Aug.21, 1956

